Cracks in the barrel mouth usually result from opening a pen up for sac replacement. This is a highly stressed area, so simply gluing the crack is insufficient. The standard repair method is to seal the crack andline the barrel mouth with fresh material, usually brass. Such a repair leaves the barrel mouth stronger than new. Effect on value depends in large part on the extent of the sealed crack,and how obtrusive it is after repair.
Heat distortion chiefly affects plastic pens (hard rubber softens when heated, but does not shrink, so any distortion can normally be corrected easily). We don't sell pens with severe distortion, but we willsometimes list a pen that is slightly bent or which displays some mild shrinkage. Often these flaws are not readily apparent upon casual examination; we are very picky, however, and assume that at least some of our customers are equally so. Effects upon value aredifficult to assess, given that so many other sellers and buyers don't even notice low-level distortion of this sort. When we mention slight shrinkage, it usually means a very subtle narrowing, often more apparent to the touch than to the eye.
The heat affected zone (or simply HAZ) is something that occurs when metal is subject to high temperatures. It has a negative impact on the design and structure of the metal. This article discusses those effects and how to reduce them.
High temperatures can lead to hydrogen embrittlement. Phase transformation may occur in some metals due to this atomic hydrogen. This can cause hydrogen cracking even after 24 hours of the cutting process.
Failures of steel parts in service or production occur infrequently. However, when steel parts fail, the consequences are dire. Here are seven ways that steel can fail as a result of quench cracking from heat treatment.
Overheating during the austenitizing portion of the heat treatment cycle can coarsen normally fine-grained steels. Coarse-grained steels increase hardening depth and are more prone to quench cracking than fine-grained steels. Avoid overheating and overly long dwell times while austenitizing.
When looking at quench cracking failures under the microscope, cracks and crack tributaries that follow the prior austenitic grain boundaries are a pretty good clue that grain coarsening and/or its causes, such as overheating or too much time at a certain temperature, have occurred. Temper scale on the fracture surface helps the metallurgist know that the crack was present before tempering. Decarburization may show that the crack was open prior to quenching.
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An Arc Strike is a discontinuity resulting from an arc, consisting of any localized remelted metal, heat affected metal, or change in the surface profile of any metal object.Arc Strikes result in localized base metal heating and very rapid cooling. When located outside the intended weld area, they may result on hardening or localized cracking, and may serve as potential sites for initiating fracture. In Statically Loaded Structures, arc strikes need not be removed, unless such removal is required in contract documents. However, in Cyclically Loaded Structures, arc strikes may result in stress concentrations that would be detrimental to the serviceability of such structures and should be ground smooth and visually inspected for cracks.
Cold cracking which also known as delayed cracking, Hydrogen Assisted Cracking (HAC) or Hydrogen Induced Cracking (HIC) is type of defect that often develop after solidification of the weld, when the temperature starts to drop from about 190 C (375 F) but the phenomenon often arises at room temperature, and even more, and it can take up to 24 hours after complete cooling. That is why some code require testing on welding work object 48 hours after the welding process. This type of crack usually observed in HAZ especially for carbon steel which has limited hardenability. However, for other alloy steel with high degree of hardenability, cold cracking could occurs in both weld metal and HAZ. Also this crack mechanism could propagate both between grains and through grains. Factors that can contribute to the occurrence of cold crack are:
Residual tensile stress could cause crack to propagate without any applied stress. To counter this, preheating of base metal could reduce the different thermal expansion coefficient which will affected cooling rate of weld metal. The utilizing of low yield streng filler metal also preferable to combat this, because the magnitude of residual stresses can be equal to σyield of the metal. Therefore, the use of austenitic stainless steel or nickel base filler could be considered due to its ductile nature. Also, Post Weld Heat Treatment (PWHT) will release any residual stresses on weld joint.
Hardness is correlated with brittleness of material. To reduce excessive hardness, preheat and pwht method can be applied to working object. The hardness value that has lower cracking tendency is below 350 VHN
Cold cracking in steels and is associated with the formation of martensite as the weld cools. Martensite has a very low solubility of hydrogen which can make it trapped inside solid. Slower cooling rates during welding process is preferable to avoid martensite structure to form. In addition, slow cooling rate means longer time at an elevated temperature, which allows more hydrogen to escape\". Slower cooling rate is achieved by using high heat input and maintain it during welding process.
Hot cracking, also known as solidification cracking, can occur with all metals, and happens in the fusion zone of a weld. To diminish the probability of this type of cracking, excess material restraint should be avoided, and a proper filler material should be utilized. Other causes include too high welding current, poor joint design that does not diffuse heat, impurities (such as sulfur and phosphorus), preheating, speed is too fast, and long arcs.
An underbead crack, also known as a heat-affected zone (HAZ) crack, is a crack that forms a short distance away from the fusion line; it occurs in low alloy and high alloy steel. The exact causes of this type of crack are not completely understood, but it is known that dissolved hydrogen must be present. The other factor that affects this type of crack is internal stresses resulting from: unequal contraction between the base metal and the weld metal, restraint of the base metal, stresses from the formation of martensite, and stresses from the precipitation of hydrogen out of the metal.
Reheat cracking is a type of cracking that occurs in HSLA steels, particularly chromium, molybdenum and vanadium steels, during postheating. The phenomenon has also been observed in austenitic stainless steels. It is caused by the poor creep ductility of the heat affected zone. Any existing defects or notches aggravate crack formation. Things that help prevent reheat cracking include heat treating first with a low temperature soak and then with a rapid heating to high temperatures, grinding or peening the weld toes, and using a two layer welding technique to refine the HAZ grain structure.
A root crack is the crack formed by the short bead at the root(of edge preparation) beginning of the welding, low current at the beginning and due to improper filler material used for welding. The major reason for these types of cracks is hydrogen embrittlement. These types of defects can be eliminated using high current at the starting and proper filler material. Toe crack occurs due to moisture content present in the welded area, it is a part of the surface crack so can be easily detected. Preheating and proper joint formation is a must for eliminating these types of defects.
Welding methods that involve the melting of metal at the site of the joint necessarily are prone to shrinkage as the heated metal cools. Shrinkage then introduces residual stresses and distortion. Distortion can pose a major problem, since the final product is not the desired shape. To alleviate certain types of distortion the workpieces can be offset so that after welding the product is the correct shape. The following pictures describe various types of welding distortion:
Traditional welding techniques often require excessive heat input, which may result in negative effects on performance of the whole component, such as distortion and reduced mechanical properties. In contrast, the heat input of the laser beam can be accurately adjusted. It has minimal side effects on the mechanical integrity of the component, either locally treating the damaged area or improving the surface properties for a specific part in the chain of manufacturing. 1e1e36bf2d